So...... I don't think i'm the only one who sees the meaning behind that choice...?
Maybe i'm looking way too far into it but here it goes.

Monk was crippled by OCD and all his fears throughout the show, all seasons leading up until the last one. In the last few episodes he drifted away slowly from those tendencies, had closure, and somewhat overcame his OCD. If you look at the pictures it is the only one where he looks happy, he overcame everything and that was a changed Monk. He has separated from his past and is now a happy man.

TLDR: Monk overcame OCD last season and that's why its different / hes actually happy.

I always figured the creators decided to make an ironic dvd set in a way which would bug somebody on an almost OCD sort of level, before realizing that it was actually a joke referring to Monk himself.

In short, it's funny that the set doesn't match because the show is about a character with OCD.